The invention relates to a primary component for an electric machine, the primary component being formed from at least one laminated core and having at least one flux guiding element on one or both front faces to reduce the force ripple. Furthermore, the invention relates to a linear motor with a primary component of this kind.
Linear motors have a primary component and a secondary component. The secondary component in particular is located opposite the primary component. The primary component is designed for energizing with electric current. The secondary component has permanent magnets or energizable windings for example. Both the primary component and the secondary component have active magnetic means for generating magnetic fields.
For constructional reasons, permanently excited linear motors have force variations which have an adverse effect on even running and dynamics. The force variations are due in part to smaller induced voltages in the edge coils.
In order to guide the magnetic flux from the excitation field of the secondary component and main field of the primary component, toothed laminations are normally used for the wound component of the motor (primary component). A magnetic interaction takes place between the excitation poles and the toothed structure of the main field which leads to parasitic cogging forces, also referred to as passive force ripple. This results in vibrations, uneven running and tracking errors in machining processes. Furthermore, the induced voltages, i.e. the electromotive forces (EMF), in the first and last coil on the front faces of the primary component are usually less pronounced than in the middle coils due to the absence of a magnetic return path. This results in the motor not having a symmetrically induced voltage and, an additional current-dependent force ripple, also referred to as active force ripple, is produced besides force losses.
A linear motor is disclosed in U.S. Pat. No. 6,831,379 B2, the primary component of which has auxiliary teeth in addition to the main teeth on the front faces of the laminated core, the auxiliary teeth being spaced apart from the air gap between primary and secondary component by means of an additional air gap. This reduces the passive force ripple of the linear motor, i.e. the cogging force.
The disadvantage here is that, although the cogging force of the linear motor is reduced, the primary component does not have symmetrically induced voltages in the individual windings or coils, i.e. there is no reduction in the active force ripple.